Connectivity in cortico-basal-ganglia-thalamic circuit and in the computational model.

<p>A) Major connections of the basal ganglia. Arrows denote excitatory connections and lines ending with circles denote inhibitory connections. The pathway which denotes cortical feedback via the hyperdirect pathway is highlighted with dashed lines. B) Summary of selected results of Tachibana et al. [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004609#pcbi.1004609.ref014" target="_blank">14</a>], who recorded activity of STN and GPe neurons in intact monkey model of Parkinson’s disease, and after blocking various inputs to the neurons in the vicinity of the recording electrode. Red lines indicate inputs that when blocked caused suppression of beta oscillations while the blue line indicates the striatal input to the GPe that when blocked did not reduce significantly the power of beta oscillations in the activity of recorded GPe neurons. C) A <i>resonance model</i> which includes time delays between the excitatory and inhibitory populations of the cortex, time delays between STN and GPe populations, time delays in the inhibitory GPe-GPe connections and further time delays connecting the cortex to the STN. This model also includes sigmoid activation functions for the STN, GPe, E and I populations which describe the input-output relationships of neurons in the populations. <i>w</i>_<i>ij</i> and <i>T</i>_<i>ij</i> denote the strength and delay of synaptic connections between neural populations <i>i</i> and <i>j</i>, where <i>i</i> and <i>j</i> can be equal to <i>C</i> for cortex, <i>S</i> for STN or <i>G</i> for GPe. Parameters shown in green are being fitted to the data. D) A <i>feedback model</i> that is identical to the model in panel C apart from including the time delayed connection between the STN and cortex, which forms a feedback loop between STN-GPe circuit and cortex. E) A linear model with time delay only in the cortical feedback.